Tobacco expansion processes

Abstract: This invention provides improvements in tobacco expansion processes which are capable of dramatically improving tobacco throughput in high pressure tobacco impregnation systems. In accordance with various aspects of the invention, tobacco can be impregnated in a high pressure impregnation zone and removed from the zone for expansion in complete cycle times of less than one minute, typically less than about 15-30 seconds. In addition, tobacco throughputs are further improved in accordance with other aspects of the invention by achieving dramatically improved use of the available treatment space in a high pressure impregnation zone. In addition, the invention provides processes for minimizing the amount of expansion agent used to treat tobacco.

Description: The invention relates to processes for expanding tobacco. More particularly, the invention relates to processes for improving throughput and economics of tobacco expansion. Background of the Invention In the past two decades, tobacco expansion processes have become an important part of the cigarette manufacturing process. Tobacco expansion processes are used to restore tobacco bulk density and/or volume which are lost during curing and storage of tobacco leaf. In addition, expanded tobacco is an important component of many low tar and ultra-low tar cigarettes. Commercially significant tobacco expansion processes are described in U.S. Patent No. 3,524,451 to Fredrickson and U.S. Patent No. 3,524,452 to Moser et al. These patents describe processes in which tobacco is contacted with an impregnant and then heated rapidly to volatilize the impregnant and expand the tobacco. A variation of these processes is described in U.S. Patent No. 3,683,937 to Fredrickson et al. which discloses a tobacco expansion process employing an organic compound in the vapor state for impregnating tobacco. The impregnated tobacco is expanded either by heating or rapidly reducing pressure. The use of a carbon dioxide for expanding tobacco is disclosed in U.S. Patent No. 4,235,250 to Utsch; U.S. Patent No. 4,258,729 to Burde et al.; and U.S. Patent No. 4,336,814 to Sykes et al., among others. In these and related processes, carbon dioxide, either in gas or liquid form, is contacted with tobacco for impregnation and thereafter the impregnated tobacco is subjected to rapid heating conditions to volatilize the carbon dioxide and thereby expand the tobacco. In the known carbon dioxide expansion processes, it is typically necessary to heat the tobacco excessively in order to achieve substantial and stable expansion of the tobacco. This excessive heating can harm the tobacco flavor and/or generate an excessive amount of tobacco fines. In addition, those processes which use liquid carbon dioxide for impregnating tobacco typically result in impregnated tobacco in the form of solid blocks of tobacco containing dry ice, which must be broken up prior to heat treatment, thereby increasing the complexity of the process. U.S. Patent No. 4,461,310 to Zeihn and U.S. Patent No. 4,289,148 to Zeihn describe the expansion of tobacco employing supercritical nitrogen or argon impregnation of tobacco. These gases are removed from the tobacco during a rapid pressure reduction, and the tobacco is expanded by exposure to heated gas or microwave. These processes require treatment of tobacco at pressures in excess of 141 or 281 kg/cm 2 (2,000 or 4,000 psi) up to above 703 kg/cm 2 (10,000 psi) in order to achieve substantial tobacco expansion. U.S. Patent No. 4,531,529 to White and Conrad describes a process for increasing the filling capacity of tobacco, wherein the tobacco is impregnated with a low-boiling and highly volatile expansion agent, such as a normally gaseous halocarbon or hydrocarbon (e.g. propane) at process conditions above or near the critical pressure and temperature of the expansion agent. The pressure is quickly released to the atmosphere so that the tobacco expands without the necessity of a heating step to either expand the tobacco or fix the tobacco in the expanded condition. The pressure conditions of this process range from 36 Kg/cm 2 (512 psi) and higher with no known upper limit. Pressures below 142 Kg/cm 2 (2,000 psi) were used to produce satisfactory tobacco expansion without excessive fracturing. Pressures above this range were said to normally not be needed. When the time period used to increase the expansion agent pressure to the necessary pressure ranged from 1 to 10 minutes, little or no additional holding time under pressure was needed in order to achieve effective impregnation of the tobacco. U.S. Patent No. 4,554,932 to Conrad and White describes a fluid pressure treating apparatus, including a cylindrical tubular shell and a reciprocal spool assembly mounted for movement between a loading position outside the shell and a treating position within the shell. Sealing members on the spool assembly are provided for engaging the shell to form a pressure chamber. Conduits are provided to introduce processing fluids into the pressure chamber. This system thereby provided an apparatus for use in high pressure materials treatment, such as tobacco impregnation for expansion, permitting easy loading and unloading and minimizing or eliminating problems associated with sealing and locking mechanisms normally used in high pressure treatment apparatus. Accordingly, this apparatus provided a pressure vessel producing time savings and improving economics in tobacco expansion. U.S. Patent No. 5,076,293 to Kramer is directed to a process and apparatus for the treatment of tobacco material and other biological materials having a mechanism for forming a dynamic seal in which cooperating moving surfaces seal a treatment chamber. The dynamic seal system provided according to this patent is useful in treating tobacco at elevated temperature and pressure conditions, including conditions of supercritical temperature and pressure for processes including tobacco expansion. Both continual and batch processes are disclosed. For tobacco expansion the use of supercritical fluids at weight ratios relative to the tobacco, of greater than 40:1 is disclosed, and complete impregnation of the tobacco material was said to be virtually instantaneous. Greater tobacco expansion was said to be obtained when impregnation times of 1 to 10 minutes were maintained prior to depressurization. U.S. Patent No. 4,962,773 to White et al. describes a process for subjecting a cigarette rod to conditions such that the cut filler undergoes volume expansion while within the paper wrap. The use of various impregnation conditions and fluids is described in this patent, including the use of impregnation conditions conducted above supercritical pressure and temperature. A pressure vessel having a volume of 4.5 liters was employed in the working examples to impregnate the tobacco rods under supercritical conditions. Tobacco expansion processes including those described above and others, must be conducted in a batch process or continual process (Kramer U.S. Patent No. 5,076,293) when impregnation pressures substantially above atmospheric pressure are used. The batch and continual treating processes require complicated treating apparatus and increased cycle times because of the time required in opening and closing the vessels and introducing and removing impregnating agent from the vessels. Some throughput improvements have been made by modifying the various apparatus employed to decrease cycle time; however, substantial throughput improvements in the known batch systems are available according to conventional techniques primarily by increasing volumes of the individual systems and/or increasing the number of batch systems used simultaneously. It is an object of the present invention to improve tobacco throughput in a tobacco expansion process such as the process disclosed in US-A-4 531 529 disclosing the features of the preamble portion of claim 1, and in accordance with the present invention this object is achieved by the features of the characterizing clause of claim 1. Preferred embodiments of the inventive process are defined in claims 2 to 9. This invention provides improvements in tobacco expansion processes which are capable of dramatically improving tobacco throughput in high pressure tobacco impregnation systems. The tobacco can be impregnated in a high pressure impregnation zone and removed from the zone for expansion in complete cycle times of less than one minute, typically less than about 15-30 seconds; further, dramatically improved use is made of the available treatment space of the high pressure impregnation zone. In addition, the amount of expansion agent used to treat tobacco is minimized. When substantially the entire available impregnation space in a high pressure impregnation zone is filled with compressed tobacco, an expansion agent is admitted into the impregnation zone and impregnates the compressed tobacco. Typically the compressed tobacco, is compressed in an amount of at least 1.5:1, and is preferably compressed in an amount of at least 2:1-3:1 or greater. Thus, the throughput for the available space in the impregnation zone is greatly improved, e.g. by 50% to 200% or more. Despite the compression of the tobacco during impregnation, substantial tobacco expansion of at least 50%, up to and greater than 100% increase in filling capacity can be achieved in preferred embodiments. Moreover, in preferred embodiments of the invention, cycle times of less than 20 seconds can be employed for impregnating the compressed tobacco. In addition to dramatically improving available throughput for a high pressure treating vessel, this aspect of the invention can also provide a substantial decrease in the amount of expansion agent admitted to the impregnation zone during impregnation. This aspect of the invention thus provides a tobacco expansion process wherein the volume of expansion agent used to impregnate tobacco can be less than the volume of the tobacco when measured in loose, i.e. non-compacted, form. Typically, the volume of expansion agent can be about one-half or less compared to the tobacco volume. The cycle time for impregnating tobacco under conditions near or above conditions of supercritical pressure and temperature can be significantly improved by preheating the tobacco prior to introducing the tobacco into the impregnation zone. Further, it has been found that prepressurizing and preheating expansion agent to temperature and pressure conditions above supercritical values prior to admission into the impregnation zone, allows for successful tobacco impregnation with expansion agent in a matter of seconds to provide impregnated tobacco capable of substantial expansion. Complete cycle times, including supercritical fluid introduction time, impregnation time and pressure release time, of less than one minute, preferably less than 20 seconds, can be achieved in accordance with this aspect of the invention. Filling capacity increases greater than 50%, up to and exceeding 100% can be achieved at cycle times of 10-12 seconds or lower. Various apparatus can be employed in conducting the processes of the invention; a spool-type tobacco expansion apparatus of the type disclosed in U.S. Patent No. 4,554,932 to Conrad and White can be used. This apparatus can be modified to incorporate a tobacco loading means which simultaneously loads and compresses tobacco into the movable spool. An accumulator may be used to provide preheated high pressure fluid to the tobacco expansion zone. The use of the accumulator minimizes volume of stored high pressure, high temperature fluid during a high temperature, high pressure impregnation process, thereby minimizing needs for high pressure vessels and decreasing safety concerns associated with the process. In greatly preferred embodiments of the invention, propane fluid is provided at a temperature above its critical temperature and above its critical pressure for impregnating the tobacco according to the process of White and Conrad, U.S. Patent No. 4,531,529. It has now been found that use of propane at pressures above 141 kg/cm 2 (2,000 psi) reduces cycle time. By combining the various aspects of the present invention, tobacco throughput in a high pressure impregnation zone can be increased by factors in excess of 10-30 times of the throughputs described in the prior art. Thus, compressing the tobacco provides a throughput compared to normal throughput of two to three times or more. By employing preheated tobacco and/or substantially instantaneously introducing preheated, prepressurized supercritical fluid into the expansion zone, up to five or more cycles of tobacco impregnation can be completed for each minute of operation. Thus, an expansion chamber of a given volume can readily be used to impregnate loose tobacco volumes exceeding five, and preferably 10 to 15 or more times the impregnation chamber volume for each minute of operation. Brief Description of the Drawings In the drawings which form a portion of the original disclosure of the invention: Figure 1 is a schematic cross-sectional view of one preferred apparatus employed in the invention with various different operating positions being partially illustrated in phantom; Figure 2 is a schematic cross-sectional view taken along line 2-2 of Figure 1 and illustrates a tobacco compacting apparatus for introducing compacted tobacco into the impregnation space of the apparatus illustrated in Figure 1; Figures 3a, 3b, and 3c are cross-sectional views of preferred accumulators for use in the apparatus illustrated in Figure 1, and which are capable of substantially instantaneous introduction of fluids having temperatures and pressures above the supercritical temperatures and pressures thereof into the apparatus of Figure 1; Figure 4 illustrates a preferred process employing various aspects of the invention; and Figure 5 schematically illustrates a preferred control method for operating the apparatus illustrated in Figure 1. Detailed Description of the Preferred Embodiment Different process and apparatus embodiments of the invention are set forth below. While the invention is described with reference to specific processes and apparatus including those illustrated in the drawings, it will be understood that the invention is not intended to be so limited. To the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from a consideration the foregoing discussion and the following detailed description. Figure 1 illustrates a preferred apparatus employed in various aspects of the invention. The apparatus of Figure 1 is generally constructed in accordance with U.S. Patent No. 4,554,932. As shown in Figure 1, the apparatus includes a pressure vessel 10 including a cylindrical tubular shell or enclosure 12 and a spool assembly 14. The shell 12 and spool assembly 14 can be made of any suitable materials, including stainless steel, bronze and the like. The specific construction and size of the shell and spool will be sufficient to withstand the pressures contemplated within the pressure vessel as will be apparent. The spool assembly 14 includes cylindrically shaped end members 16 and 18 and a connecting rod 20 . When the spool is within the shell 12 as illustrated in Figure 1, the end members 16 and 18 , the connecting rod 20 and the shell 12 define an annular space 22 of predetermined volume constituting a sealed pressure chamber or zone. As illustrated in Figure 1, the spool assembly is positioned horizontally and is arranged for reciprocating movement between a loading position 24 , illustrated in phantom, an unloading position 26 , also illustrated in phantom, and the impregnating position specifically shown in Figure 1. A hydraulic piston or similar motor means 28 is axially attached via a shaft 30 partially shown in Figure 1 for moving the spool among the three positions. Tobacco is loaded onto the spool in position 24 by means of a pair of opposed semi-cylindrical loading members 32 . The tobacco can be in any of various forms including the form of leaf (including stem and veins), strips (leaf with the stem removed), or cigarette cut filler (strips cut or shredded for cigarette making). The loading members 32 are connected via rods 34 to a reciprocating force means, not shown, such as a hydraulic piston or the like. Separate charges of tobacco 36 are forced onto the spool 14 , preferably to compress the tobacco as discussed in greater detail below in connection with Figure 2. Following loading of the spool at position 24 , the spool is moved to the impregnating position. Each of the end members 16 and 18 include inflatable sealing members 40 and 42 , respectively. The sealing members are formed of hydraulically inflatable elastomeric rings which receive a hydraulic fluid via fluid lines 44 . Hydraulic fluid, such as food grade oil, is forced through the lines 44 by a hydraulic accumulator 45 , and into the sealing members 40 causing same to expand outwardly and seal the pressure chamber 22 against leaks. The sealing members also advantageously include integral wear rings, not shown, which serve to scrape tobacco particles off of the inside surface of shell 12 and tobacco loading members 32 as the spool moves from position to position. Hydraulic fluid is introduced into line 44 from one end of the spool via a bore through a connecting rod 46 , partially illustrated in Figure 1 and which is connected to at least one end of the spool 14 . High pressure gas lines 48 and 49 communicate through the shell 12 via ports 50 and 51 which are aligned with an annular space 52 formed on end member 18 between sealing members 42 . The annular space 52 is connected via a plurality of radial ports 54 and axial ports 56 with grooves 58 formed in the surface of connecting rod 20 . The ports 50 and 51 thereby allow for the introduction and removal of high pressure fluid into and out of the pressure chamber 22 when the spool member 14 is in the position shown. One or more screens 59 surround the connecting rod 20 to prevent tobacco from clogging the ports 56 and grooves 58 . A pair of fast acting valves 60 and 62 are provided for rapid introduction and release of fluid into and out of the impregnating chamber 22 . These valves are preferably ball valves having a port size ranging from 1,27 cm to 3,81 cm (1/2 inch to 1.5 inch) in diameter or greater depending on the size of the impregnation zone 22 to thereby provide for substantially instantaneous admittance and removal of high pressure fluid to and from the impregnation zone 22 . The valves are advantageously automatically opened and closed by fast acting hydraulic actuators, not shown. On the input side, the high pressure gas line 48 is connected to an accumulator device 64 discussed in greater detail below. A vaporizer 66 is provided for heating gas fed to the accumulator 64 . Accumulator 64 may also be heated by means not shown to maintain the fluid within the accumulator in heated condition. A high pressure pump, not shown, is provided upstream of vaporizer 66 for feeding high pressure fluid at, e.g., 176 kg/cm 2 above ambient pressure (2,500 psig) to vaporizer 66 and accumulator 64 . The high pressure line 49 , which is used to remove high pressure fluid from the impregnation zone 22 is connected to a gas recovery zone (not shown) for recovery of fluid removed from the impregnation zone. A pneumatic unloading device such as an oil free compressor 72 is provided in tobacco unloading zone and directs fluid such high pressure an or nitrogen onto the tobacco surrounding spool 14 when the spool is moved to and from the unloading position 26 . Tobacco removed in unloading position 26 is received in a detangler unit 73 comprising intermeshing oscillating tines and is then fed to a recovery chute 74 wherein the tobacco may be further treated for drying, or heated for expansion, if desired. Figure 2 schematically illustrates the tobacco compression loading means 32 , which are used to compress tobacco around the spool 14 . As shown, each of the loading members 32 are semi-cylindrical members mounted for movement between a withdrawn position and a closed position 80 , illustrated in phantom. Tobacco 36 is fed via chutes 82 into the tobacco loading zone. The cylindrical members 32 are thereafter moved to loading position 80 to press the tobacco 36 onto the spool member 14 , thereby substantially filling the annular space between the end members 16 and 18 and surrounding the connecting rod 20 . The amount of tobacco 36 is preferably an amount such that its volume when measured in loose form, prior to loading onto the spool 14 is substantially greater than the volume of this annular space. The tobacco volume prior to compression, or loose fill volume of the tobacco, is determined by measuring the tobacco density in a cubic container of 30,5 x 30,5 x 30,5 cm (one foot by one foot by one foot). Tobacco is poured into the cubic container and weighed to determine the loose fill density of the tobacco. The loose fill volume of a tobacco charge prior to compression onto the spool then can be determined from the weight of the charge and the loose fill density value of the tobacco. The loose fill volume of the charge is divided by the compressed volume of the tobacco charge, i.e., the volume on the spool, to determine compression ratio. All values are determined at, or corrected to, the actual moisture of the tobacco charge fed to the impregnation zone. Thus, for a spool having an impregnation volume of 410 cm 3 (25 cubic inches), compressing tobacco having a loose fill volume of 820 cm 3 (50 cubic inches) onto the spool, would result in a compression ratio of 2:1. It will be apparent that the volume available on spool 14 for occupation by tobacco will be less than the total space available for occupation by high pressure fluid. In this regard, the spool includes fluid ports 54 and 56 and channels 58 which constitute space available to the fluid but which cannot be occupied by tobacco due to the presence of the screen 59 . Thus, the "available volume" for occupation by tobacco, i.e., the volume which available for occupation by tobacco tightly packed into impregnation zone 22 , is typically less than the volume available for occupation by impregnation fluid. Typically, the available volume for occupation by tobacco is about 75-80% of the volume available to the impregnation fluid, the latter including the space defined by the various channels and ports, which is not available to the tobacco. Figures 3a, 3b and 3c are cross-sectional views of preferred accumulators for use in the apparatus illustrated in Figure 1, and which are capable of substantially instantaneous introduction of fluids having temperatures and pressures above the supercritical temperatures and pressures thereof into the apparatus of Figure 1. Figure 3a illustrates a preferred gas/gas accumulating device which is useful in accordance with the invention. The accumulator 64 is used to provide a high pressure, high temperature impregnation fluid, such as propane at 176 kg/cm 2 above ambient pressure (2,500 psig) and at a temperature above about 200°F (93°C), to the impregnation zone in the spool impregnator shown in Figure 1. The accumulator 64 includes a tubular shell 100 formed of a material capable of withstanding high temperatures and pressures, such as a high grade carbon steel and which has been hardened on its inside surface 102 . At each end of the accumulator there are end members 104 and 106 including ports 108 and 110 , respectively, for admitting high pressure gas. The end members are secured by threads 112 in the ends of the shell 100 . Mounted on each end member is a shock absorbing device, including an annular member 114 supported by a pair of flange springs 115 in the form of Bellville washers. A centrally located piston member 116 is mounted for movement within the cylinder 100 and defines two separate fluid zones 118 and 120 on the opposed sides thereof. The piston member 116 is prepared from a suitable material such as phosphor bronze. A slideable sealing member 119 is provided about the exterior periphery of the piston member 116 . The sealing member 119 is capable of providing and maintaining a seal between zones 118 and 120 during motion of the piston 116 , under the pressure and temperature conditions described above. The sealing member is inert, and is flexible, capable of radial outward expansion to form a sealing force between the exterior of the piston 116 and the inside surface of the shell 100 . An exemplary sealing member 119 is illustrated in Figure 3a as five separate carbon packing rings 120' and 121 to 124 surrounding the periphery of the piston 116 and providing for sealing contact between the exterior periphery of the piston 116 and the interior of the shell 100 . The three inside piston rings 121-123 are more flexible than the exterior piston rings 120' and 124 . These packing rings are molded from GRAFOIL carbon and are commercially available from A.W. Chesterson Company as NS Style 5300 Solid Die Formed Rings ( 121-123 ) and NS Style 5600 GTP HD Solid Die Formed Rings ( 120' , 124 ). However, other materials which are inert and capable of providing a seal between zones 118 and 120 during movement of the piston 116 can be used. The packing rings 120' and 121 to 124 are maintained under compression by an annular ring member 126 , which is forced axially against the rings by the ears 128 of an annular forcing member 130 . The forcing member 130 is secured to the piston member 116 by a threaded bolt 132 and applies a predetermined biasing force due to biasing members 134 which are 19 mm (3/4 inch) flange springs commercially available from A.W. Chesterson Company as Style 5500 3/4 inch Flange Springs. The compression force applied via bolt 132 , compression member 130 and annular ring 126 to the packing rings 122-124 is the amount of force just sufficient to flatten the two flange springs 134 by tightening of the bolt 132 . This results in a radially outward expansion of the packing rings 120' and 124 , which thereby form a sealing force between the exterior periphery of the sliding piston 116 and the interior periphery of the shell 100 . In the apparatus of Fig 3A an inert high pressure gas, such as nitrogen at a pressure of 422 kg/cm 2 above ambient pressure (6,000 psig), is maintained in one fluid chamber, 118 , while impregnation fluid, such as propane, at 176 kg/cm 2 above ambient pressure (2,500 psig) is maintained in the second fluid zone 120 . When high pressure impregnation fluid is released from the zone 120 into the impregnator illustrated in Figure 1, the piston 116 can be moved rapidly into contact with end member 114 and the force is absorbed by the force-absorbing members 115 . Thereafter, impregnation fluid is pumped back into the accumulator until the predetermined pressure, preferably, 176 kg/cm 2 (2,500 psi), is reached. Figure 3b illustrates another embodiment of an accumulator, which is operated by meeans of a hydraulic fluid, which is also useful in accordance with the present invention. As with the accumulator illustrated in Figure 3a, the accumulator 64 of Figure 3b is used to provide a high pressure impregnation fluid, such as propane at 176 kg/cm 2 above ambient pressure (2,500 psig), to the impregnation zone in the spool impregnator shown in Figure 1. The accumulator 64 is substantially similar in many respects in structure to the gas/gas accumulator illustrated in Figure 3a above. For example, the accumulator 64 illustrated in Figure 3b includes a tubular shell 100 , end members 104 and 106 , including port 110 for admitting high pressure gas and a shock absorbing device, including an annular member 114 supported by a pair of flange springs 115 in the form of Bellville washers. The end members 104 and 106 are configured as described above with regard to the accumulator of Figure 3a, except that end member 104 does not include port 108 for admitting high pressure gas. Also as illustrated, the shock absorbing device can include shock absorbing ears 300 . The accumulator of Figure 3b is operated using hydraulic fluid. The accumulator 64 includes a conventional hydraulic piston member 302 connected by a common rod 304 to a piston member 116 . Piston member 116 of Figure 3b has a structure substantially the same as that described above with regard to centrally located piston member 116 in Figure 3a, except that one end thereof is attached to one end of the common rod 304 . A centrally located stationary stop member 306 is fixedly mounted within the cylinder 100 and defines fluid zones 118 and 120 on opposed sides thereof. Stationary piston member 306 includes an aperature 307 adapted for recieving rod 304 which, in turn, moves axially in reciprocal motion therethrough. Fluid zone 118 includes port 308 for admitting and removing hydraulic fluid, such as food grade oil, into and out of fluid zone 118 . Hydraulic fluid is forced through inlet port 308 into fluid zone 118 , so as to maintain impregnation fluid, such as propane, at a pressure of 176 kg/cm 2 above ambient pressure (2,500 psig) in the second fluid zone 120 . When high pressure impregnation fluid is released from the zone 120 into the impregnator illustrated in Figure 1, the piston 116 can be moved rapidly into contact with end member 104 and the force is absorbed by the force-absorbing members 115 , as described above. Thereafter, impregnation fluid is pumped back into the accumulator until the predetermined pressure, preferably 176 kg/cm 2 (2,500 psi), is reached. Stationary piston member 306 also separates any propane leaks from any hydraulic fluid leaks. Any propane leaks are directed via port 310 to a propane recovery zone. Here the propane can be burned or vented, for example, to the gas recovery zone for recovery of fluid removed from the impregnation zone, as described above, or to recovery chute 74 . Any hydraulic fluid leaks are directed via port 312 to a hydraulic fluid recovery zone, for example to a hydraulic fluid holding tank (not shown). Also as illustrated in Figure 3b, the accumulator can include a heating jacket 314 about the outer periphery of cylinder 100 . Heating jacket 314 can be any of the types of devices known in the art for heating fluid and/or maintaining the temperature of a fluid within in a vessel. In this invention, heating jacket 314 is used to heat the impregnation fluid in fluid zone 120 . Accordingly, advantageously the heating jacket extends along the length of the impregnation fluid zone 120 , as illustrated in Figure 3b. As will be appreciated by the skilled artisan, heating jacket 314 can also extend the entire length of the accumulator cylinder, as illustrated in Figure 3c. Heating jacket 314 provides heat conventionally, for example, by the introduction and removal of heated oil via lines 316 and 318 , respectively. Figure 3c illustrates yet another embodiment of an accumulator which is useful in accordance with the present invention. As with the accumulators illustrated in Figures 3a and 3b, the accumulator 64 of Figure 3b is used to provide a high pressure impregnation fluid, such as propane at 176 kg/cm 2 above ambient pressure (2,500 psig), to the impregnation zone in the spool impregnator shown in Figure 1. Also as with the accumulator illustrated in Figure 3b, the accumulator 64 of Figure 3c is substantially similar in many respects in structure to that illustrated in Figure 3a above. The accumulator illustrated in Figure 3c includes a tubular shell 100 , end members 104 and 106 , including port 110 for admitting high pressure gas, and a centrally located piston member 116 . The piston 116 defines two separate zones, zone 118 and at least one fluid zone 120 , on the opposed sides thereof. The end members 104 and 106 and piston 116 are configured as described above with regard to the accumulator of Figure 3a, except that end member 104 does not include port 108 for admitting a high pressure gas. In this embodiment of the invention, end member 104 is modified to include an aperature 320 which is adapted for reciprocal movement therein of a connecting rod 322 as described in more detail below. In addition, piston 116 is adapted at one end thereof for attachment to the connecting rod 322 , also as described in more detail below. In Figure 3c, a hydraulic actuator or similar motor means 324 is coupled to piston 116 via connecting rod 322 for moving the piston 116 within the accumulator 64 . Hydraulic actuator 324 can be any of the types of hydraulic actuators known in the art for converting hydraulic power into mechanical work. For example, as illustrated, hydraulic actuator 324 can include a tubular shell 326 . At each end of the hydraulic actuator 324 are end members 328 and 330 . A centrally located piston member 332 is mounted for movement within the cylinder 326 and defines two separate hydraulic fluid zones 334 and 336 on the opposed sides thereof. Each of zones 334 and 336 includes ports 338 and 340 , respectively. Port 338 admits hydraulic fluid from a hydraulic fluid supply 342 via line 344 , while port 340 returns hydraulic fluid to hydraulic fluid supply 342 via line 346 , as indicated by the arrows. Hydraulic actuator 324 also includes a connecting rod 348 which extends axially from piston 332 through fluid zone 334 and through an aperature 350 in end member 328 . Connecting rod 348 is coupled with connecting rod 322 so that reciprocal movement by connecting rod 348 translates into reciprocal movement of connecting rod 322 , and thus movement of piston 116 within cylinder 100 . As noted above, impregnation fluid, such as propane, at 176 kg/cm 2 above ambient pressure (2,500 psig) is maintained in the second fluid zone 120 . When high pressure impregnation fluid is forced by the hydraulic actuator 324 from the zone 120 into the impregnator illustrated in Figure 1, the piston 116 can be moved rapidly into contact with end member 114 and the force is absorbed by the force-absorbing members 115 . Thereafter, impregnation fluid is pumped back into the accumulator until the predetermined pressure, preferably 176 kg/cm 2 (2,500 psi), is reached. Returning to Figure 1, in operation, a high pressure pump, not shown, is used to provide propane to the high pressure fluid zone of accumulator 64 . When a gas is discharged from the accumulator, the pressure loss is sensed by means not shown and a control activates the pump which immediately starts refilling the accumulator with high pressure fluid, such as propane. The gas accumulator 64 can be refilled in a short period of 5-30 seconds, during the period employed in the present invention for impregnating the tobacco in impregnation zone 22 of Figure 1. Figure 4 illustrates one preferred process of the invention. Preferably the process of Figure 4 is conducted in accordance with U.S. Patent No. 4,531,529. A high pressure, high temperature propane storage unit, such as accumulator 64 of Figure 3, is provided as shown in Block 150 . The storage unit 150 can take forms other than accumulator 64 . For example, a high volume surge tank is also contemplated for storage of high temperature, high pressure propane. Alternatively, a Metal Bellows accumulator available from Parker Bertea Aerospace, Parker Hannfin Corp., Metal Bellows Division, Moorpark, California, is contemplated for use herein. The pressure of the propane is maintained preferably above 141 kg/cm 2 (2,000 psi), advantageously between about 176 and 211 kg/cm 2 (2,500 psi and 3,000 psi). In accordance with the present invention, it has been found that extremely short impregnation times, between about 5 and about 15 seconds, can be used to impregnate tobacco when these high pressures are used, while obtaining extremely desirable increases in tobacco filling capacity, for example, in excess of 50 to 100% increase in filling capacity. The temperature of the propane is advantageously maintained above 280°F (138°C), preferably between about 300°F (149°C) and 400°F (204°C), e.g., about 300-315°F (149-157°C) . This provides excess sensible heat for heating the tobacco in the impregnation zone. As indicated in Block 155 , tobacco preferably in the form of cut filler is advantageously preheated prior to introduction into the impregnation zone. Preheating of the tobacco also provides heat for establishing proper short cycle time conditions in the impregnation zone. Preferably, the tobacco is preheated to a temperature above about 125°F (52°C), more preferably a temperature of about 140°F (60°C) or greater e.g., to a temperature of 150°-160°F (66°-71°C) or higher. Extra moisture can be added to the tobacco to increase the pliability of the tobacco. Moisture contents between about 16%, up to about 30% or more, are advantageously used in the invention. Preheating of the tobacco can be conducted by any of various means including the use of heated drums, microwave energy and steam injection. Steam heating is believed to be preferable because heat is more effectively transferred to the tobacco, while at the same time the moisture level can be increased. The preheated tobacco is thereafter compressed as indicated in Block 160 . As discussed previously, the tobacco is compressed at a compression ratio of at least about 1.5:1, more preferably above 1.5:1. Advantageously, the tobacco is compressed to a compression ratio of greater than 2:1, up to ratios amounts of 3:1 and greater. Compression of the tobacco increases the tobacco density so that the density of the tobacco fed into the impregnation zone is substantially greater than the tobacco density prior to compression. Those skilled in the art will be aware that loose fill tobacco densities can vary greatly depending on whether the tobacco is in leaf form or in cut filler form; the type of tobacco, the moisture content of the tobacco, and other factors. Packing densities of 0,32 g/cm 3 (20 pounds per cubic foot), calculated based on a moisture content of 12% are readily employed in the present invention. Although increasing the packing density can, to some extent, increase the cycle time for achieving identical amounts of expansion, packing densities in excess of 0,4 g/cm 3 -0,48 g/cm 3 (25-30 pounds per cubic foot) calculated based on 12% moisture and higher have also been successfully used in the present invention while achieving impregnation times of below 20 seconds and filling capacity increases in excess of 50-100%. The compressed tobacco is thereafter impregnated in the impregnation zone as indicated in Block 165 . When propane is used as the impregnating fluid, the cumulative amount of heat supplied to the impregnation zone from the heated propane and the preheated tobacco is advantageously sufficient to provide impregnation conditions in the impregnation zone of between about 240°F (116°C) and about 270°F (132°C), preferably about 260°F (127°C). It has been found that impregnation at temperature and pressure conditions of about 260°F (127°C) and 176 kg/cm 2 above ambient pressure (2,500 psig) can be achieved in about 5 seconds or even less when the heat is supplied by both the preheated tobacco and preheated propane. It will be apparent that, when the propane fluid is heated to higher temperatures the tobacco can be heated to a lesser degree to provide the desirable temperature conditions in the impregnation zone. However, there is believed to be an upper limit of temperature for the propane above which the tobacco in the impregnation zone might be harmed. In addition, because low volumes of impregnation fluids are used in preferred embodiments of the present invention, the mass of the impregnation fluid available for heating of the tobacco is relatively low. The expansion agent mass is typically about the same or less than the mass of the tobacco. Thus, the addition of heat from a source such as the tobacco is desirable. It will also be apparent that temperature conditions in the tobacco impregnation zone can be achieved by other means, such as by employing a heater in the impregnation zone. However, for extremely short cycle times, the combination of preheated tobacco and preheated high pressure propane has been found to produce extremely desirable results. The advantageous effects of preheating the tobacco are not fully understood. However, it is possible that preheated tobacco might absorb impregnation fluid at a faster rate than ambient temperature tobacco due to factors including pliability of the tobacco. The compressed and impregnated tobacco is maintained under impregnation conditions for a short period of time ranging from 1-2 seconds up to about twenty seconds. As shown in Block 170 of Figure 4, thereafter the pressure is released. Preferably, pressure release is substantially instantaneous, i.e., is achieved in about one second or less. This can be achieved by employing a fast acting valve having a large port for rapidly releasing pressure. The compressed tobacco is then substantially immediately removed from the impregnation zone so that expansion of the tobacco can be effected. Preferably, the tobacco is treated by contact with forced dry air or heated air in order to establish a moisture content of, for example, about 10-12% moisture which helps stabilize the tobacco in expanded form. When the expansion agent is propane or a similar expansion agent of the type disclosed in U.S Patent No. 4,531,529 to the White and Conrad, no heating of the tobacco is necessary in order to fix the tobacco in expanded form. Moreover, there is no substantial loss of volatile flavoring agents, sugars or the like, because of the lack of high temperature heating conditions. However, the invention can also be employed in connection with other expansion agents including those which require the use of expansion conditions including heat in order to achieve or fix expansion of the tobacco. Figure 5 illustrates a control method used in connection with the apparatus of Figure 1 to achieve substantial expansion of tobacco in short cycle times of less than twenty seconds. This or a similar control system including sensors for sensing conditions during the expansion process are extremely desirable in order to achieve cycle times of twenty seconds or less. Control hardware can be pneumatic, electric or pneumatic and electric based and can include a microprocessor as will be apparent to those skilled in the art. With reference to Figure 5, in Block 200 appropriate sensors are used to verify that the spool is in the loading position 24 and that an appropriately sized charge of tobacco is in position for loading. If these conditions are satisfied, control passes to Block 205 and the loading members 32 are moved to force tobacco onto the spool 14 . An appropriate sensing mechanism such as a proof of position valve senses the presence of both loading members 32 in the appropriate loading position and control is then passed to Block 210 . In Block 210 , the hydraulic piston 28 is activated to move the spool into the pressure shell 12 . An appropriate sensor such as a proof of position valve or the like senses the position of the spool in the proper location in shell 12 and control is then passed to Block 215 . In Block 215 , a valve is opened to allow hydraulic fluid from hydraulic accumulator 45 to fill seals 40 and 42 . The hydraulic accumulator 45 preferably holds sufficient amount of hydraulic fluid to pressurize each of seals 40 and 42 to a pressure of 211 kg/cm 2 (3,000 psi) during a time period of about one second or less, preferably substantially less than one second. An appropriate sensor senses the fluid pressure of fluid within the seals 40 and 42 and when the pressure is at the desired pressure, for example, 211 kg/cm 2 (3,000 psi), control is passed to Block 220 . In Block 220 , the fast acting fill valve 60 is opened and a timer is activated. This allows heated and pressurized impregnation fluid, such as propane at a pressure above 141 kg/cm 2 above ambient pressure (2,000 psig) and a temperature of about 300°F (149°C) or greater to enter into the impregnation zone 22 . Under these conditions, and particularly when the tobacco in the impregnation zone has been preheated, the impregnation is quite rapid so that the timer can be set for a short period of between several seconds and about 15-20 seconds. The timing for impregnation can be adjusted based on moisture conditions, temperature conditions and density conditions of the tobacco in the impregnation zone 22 . When the timer reaches the set time period, control passes to Block 225 wherein the fill valve is closed. A sensor verifies that this valve is closed and control is immediately passed to Block 230 for rapid opening of the vent valve 62 . Control then passes to Block 235 wherein a pressure sensor within the impregnation zone is repeatedly read until the pressure in the impregnation zone has dropped to a predetermined low pressure, for example 7 to 14 kg/cm 2 above ambient pressure (10-20 psig). At this point, control is passed to Block 240 wherein a valve is opened to allow hydraulic fluid to be removed from seals 40 and 42 . An appropriate sensor senses the pressure of the hydraulic fluid in the seals and when the fluid pressure has reached a desirably low pressure, control is passed to Block 245 . In Block 245 , the hydraulic piston 28 is activated to move the spool 14 to the unloading position 26 . At the same time, the compressor 72 is started for directing high pressure air or nitrogen onto the spool as it is moved into position 26 . In Block 250 an appropriate sensor senses the position of the spool when it reaches the fully extended unloading position and the hydraulic piston 28 then immediately changes the direction of motion of the spool for return to the loading position 24 . Control is next passed to Block 255 wherein a sensor detects the position of the spool in chamber 12 and the compressor 72 is then deactivated. The control sequence is then started again beginning with Block 200 . The various aspects of the tobacco expansion processes described herein have been discussed specifically in connection with the use of propane as an expansion promoting impregnation agent and the use of impregnation temperature conditions near or above supercritical temperature together with conditions of elevated pressure approaching or above supercritical pressure, and in connection with preferred apparatus. However, various significant tobacco expansion processes and apparatus disclosed herein are also considered applicable to other tobacco expansion processes, expansion fluids, and apparatus. For example, tobacco compression can substantially improve the throughput of many tobacco impregnation processes conducted in various vessels at high pressures of, e.g. 70 kg/cm 2 above ambient pressure (above 100 psig), for subsequent tobacco expansion. Similarly, the use of volumes of tobacco expansion agents which are substantially less than the volume of the loose fill volume of the tobacco admitted into the impregnation zone can improve the economics of many tobacco impregnation and expansion processes, including processes where the expansion agent in the impregnation zone is present during impregnation as a gas or liquid or both. Similarly, substantially instantaneous introduction into the impregnation zone of high temperature, high pressure impregnating fluids near or above conditions of both supercritical temperature and pressure, can be used to significantly shorten the impregnation time period necessary prior to a subsequent heating step. Likewise, where the impregnating fluid is employed to impregnate the tobacco under elevated temperature conditions, the tobacco preheating step of this invention can significantly improve the impregnation cycle time. Tobacco filling capacities when referred to herein, are measured in the normal manner using an electronically automated filling capacity meter in which a solid piston, 9,21 cm (3.625 inches) in diameter, is slideably positioned in a similarly sized cylinder and exerts a pressure of 0,183 kg/cm 2 (2.6 lbs. per sq. in.) on a tobacco sample located in the cylinder. These parameters are believed to simulate the packing conditions to which tobacco is subjected in cigarette making apparatus during the formation of a cigarette rod. Measured tobacco samples having a weight of 50g are used for expanded tobacco. Samples having a weight of 100g are used for unexpanded tobacco.

Claims: A process for increasing the filling capacity of tobacco by volume expansion of said tobacco, the process comprising the steps of placing into an impregnation chamber capable of withstanding elevated pressure conditions a charge of tobacco to be expanded, impregnating said tobacco charge in said chamber with propane as an expansion agent under conditions sufficient to provide impregnated tobacco capable of expanding at least about 50 % when exposed to expansion conditions, and removing the impregnated tobacco charge from said chamber and subjecting the impregnated tobacco to conditions sufficient to expand the tobacco, characterized in that for impregnating the tobacco to be expanded said tobacco is compressed at a compression ratio of at least 1,5 : 1 relative to the loose fill volume of the tobacco to be expanded, and that the available impregnation volume of said chamber is substantially filled with said compressed tobacco to be impregnated. The process of claim 1, wherein said compression ratio is at least 2 : 1, preferably at least 3 : 1. The process of claim 1 or 2, wherein said impregnation step is conducted under temperature conditions at or above about the supercritical temperature of the expansion agent. The process of one or several of claims 1 to 3, wherein said impregnation step is conducted at or above about the supercritical pressure of the expansion agent. The process of one or several of claims 1 to 4, wherein the tobacco to be impregnated is preheated to an elevated temperature prior to being placed in said impregnation chamber. The process of claim 5, wherein the tobacco is preheated to a temperature of at least 52°C. The process of one or several of claims 1 to 6, wherein said impregnation step is conducted during a period of less than one minute. The process of one or several of claims 1 to 7, wherein the expansion agent is admitted into the impregnation chamber as a fluid having a temperature above the supercritical temperature of the fluid and a pressure above the supercritical pressure of the fluid. The process of one or several of claims 1 to 8, wherein the propane is introduced into the impregnation chamber at a pressure above about 142 kg/cm 2 above ambient pressure (2000 psig) and at a temperature above about 116°C (240°F).

Inventors: CONRAD LUCAS JONES, WHITE JACKIE LEE, CONRAD, LUCAS JONES, WHITE, JACKIE LEE
Applicants: REYNOLDS TOBACCO CO R, R.J. REYNOLDS TOBACCO COMPANY
Application year: 1994
Main classification: A24B3
IPC codes: A24B3